1. Field of the Invention
The present invention relates to a spherical motor, and more particularly, to a spherical motor rotating in multiple degrees of freedom, wherein the rotor has a reliable capability to determine positioning.
2. Description of the Related Art
The term “humanoid” normally refers to a robot resembling a human, which has locomotive organs moving like those of the human, sense organs resembling those of the human, and intellectual organs capable of deciding, thinking, and feeling like a human.
Technologies related to the humanoid have been developed in the direction of realizing the humanoid's actions more smoothly so that they more closely resemble those of a human and enhancing the efficiency of the machineries by minimizing the size of the components. Especially, as the motor is the most important component among those which are in charge of the locomotive organs, a new motor with new degrees of freedom is needed to achieve the minimization and the high efficiency in addition to the smooth movements breaking away from the conventional characteristic of one degree of freedom.
FIG. 13 is a perspective view illustrating a drive system of the prior art to realize multiple degrees of freedom movement.
As illustrated in FIG. 13, the drive system of the prior art has a multi-frame structure and each frame is connected with a motor to generate power. This drive system needs to use a plurality of motors to realize the multi-degrees of freedom of movements. Consequently, there is a limit because weight and volume several fold larger than the drive system of one degree of freedom are needed to generate the desired output.
Robot's joint regions such as the arm, wrist, shoulder, and pelvis have a very complicated drive mechanism since multi-drive systems in multi degrees of freedom need to be intensively embodied at each connecting point, and the overall robot's size becomes bigger to secure enough space for installing a plurality of motors therein.
A spherical motor can be broadly used to solve this kind of problem. FIG. 14 is a perspective view illustrating a frame of a normal spherical motor, FIG. 15 is a schematic view showing coils and a rotor of the normal spherical motor, and FIG. 16 is a diagram illustrating the resultant torque by a synthesized magneto-motive force between the coil and the permanent magnet of the normal spherical motor.
The supporting frame of the spherical motor can eliminate the limit to the slope of a rotating shaft when it is structured with a spherical bearing and a round rotor. However, a framed embodiment with the supporting structure will be described below as illustrated in FIG. 14 for the purposes of understanding the invention and convenient description.
As shown in FIG. 14, a supporting structure of the spherical motor having three degrees of freedom includes more than two rotatable frames 3 and 5 like a gyroscope, and the spherical motor formed with a stator 10, a rotor 20, and a shaft 30 is supported inside the frames 3 and 5.
As illustrated in FIG. 15, the spherical motor 1 supported inside the frames 3 and 5 includes the stator formed as a hollow sphere; the rotor 20 rotatably installed in the stator 10; and the shaft 30 which is a center axle and transmits the rotating power to the outside. The three degrees of freedom of movement of the rotor 20 are possible since a plurality of coils 12 and 14 is dispersed on the inner surface of the stator 10. The shaft 30 can be inclined in any direction because the permanent magnets 22 are formed at the opposing sides of the rotor 20.
As will be described in detail below, six coils 12 and 14 are respectively arranged on the top portion and bottom portion of the inner surface of the stator 10 at regular intervals and controlled by the 12-channels of current source. The rotor 20 is formed in a “+” shape and four permanent magnets 22 are installed at each end, and permanent magnets 22 can only turn on the shaft 30 since they are fixed on the shaft although they can rotate in any direction.
The coils 12 and 14 formed on the inner surface of the stator 10 are the electromagnets distanced from the permanent magnets 22 at regular air gaps. The electric current circulated into the coils 12 and 14 generates a synthesized magneto-motive force, which positions the location of the electromagnets. The rotor 20 as well as the permanent magnet 22 can be rotated or be inclined in any direction according to the location of the coils 12 and 14. In other words, the rotor 20 can be rotated and inclined in the desired direction if the current value into each coil 12 and 14 can be properly controlled. It is understood that the rotation and position determination of the rotor 20 can be much affected by the coil 12 and 14 of the stator 10.
Referring to FIGS. 15 and 16, the synthesized magneto-motive force between the coil 12 and 14 and the permanent magnets 22 located inside the spherical motor 1 as above mentioned will be described below.
As described in FIGS. 15 and 16, the corresponding torques to the magneto-motive force by the coil 12, (hereinafter, referred to as ‘upper coil’) installed on the upper inner surface of the stator 10 on the basis of ‘X-Y plane’ will be graphed as the first line 42 and the corresponding torques to the magneto-motive force by the coil 14, (hereinafter, referred to as ‘bottom coil’) installed on the bottom inner surface of the stator 10 will be graphed as a second line 44. At this time, the resultant torque like a synthesized third line 46 from the first line 42 and the second line 44 will be shown since the magneto-motive forces by the upper coil 12 and the bottom coil 14 are working together.
If the slope of the resultant torque is a positive (+) sign in the region of drawing number 48, it means that it will easily rotate into the positive direction from the current position when an external force is applied; and if the slope of the resultant torque is a negative (−) sign, it means that it will return to the current position even though an external force is applied. Since the slope of the resultant torque in the spherical motor 1 is a positive, it is understood that it has an unstable position determination.
In order to get a stable position determination of the rotor 20, the slope of the resultant torque by the coil 12 and 14 needs to be a negative (−). For this job, more numbers of coils than those illustrated in FIG. 15 are used or the weight of the central axis needs to be corrected. However, when more numbers of coils are used, the control system to control the flowing current in each coil can be complicated and the number of the drive system needs to be increased. When the weight of the central axis is corrected, an extra space for the balance weight is needed.
FIG. 17 is a perspective view illustrating the permanent magnets of the rotor and some parts of the coils in order to describe the generation principle of the synthesized magneto-motive force in the normal spherical motor, and FIG. 18 is a diagram showing the changes of the resultant torque by the synthesized magneto-motive force according to the coil position of the normal spherical motor.
When the upper coil 12 and the bottom coil 14 move in the A1 direction and the B1 direction so that the angle formed by the center of the magneto-motive force from the upper coil 12 and the center of the magneto-motive force from the bottom coil 14 is getting smaller, the peak of the corresponding torque 42 to the magneto-motive force by the upper coil 12 is moving in the A2 direction and the peak of the corresponding torque 44 to the magneto-motive force by the bottom coil 14 is moving in the B2 direction as illustrated in FIG. 18. Consequently, the slope of the resultant torque changes from positive (+) to negative (−) and arrives at the stable position determination.
However, there is a limit of decreasing the angle between the center of the magneto-motive forces by each coil 12 and 14 when the upper coil 12 and the bottom coil 14 are located in the same level.